Electrophysiological and optical recording techniques are used primarily to elucidate the development, differentiation and cellular distribution of physiologically important properties expressed in vitro by vertebrate CNS neurons or by fibroblasts transfected with transmitter receptor genes. Electrical studies involve direct, high-fidelity amplification of ion fluxes generated either in single cells or patches or in synaptically coupled pairs of cells maintained in monolayer culture. Optical recordings include indirect measurements of membrane potential or of intracellular ion concentration in small populations (50-100) of cells in culture. Principal findings this year include: 1) depolarizing GABA-A receptors are coexpressed at E13 along with functional voltage-dependent Na+ channels and depolarizing kainic acid receptors in postmitotic neurons of ventral cervical rat spinal cord; 2) GABA-A receptors couple to Cl- ion selective channels with complex kinetics in cultured embryonic spinal hippocampal and cordical neurons; 3) GABA-A receptors activated synaptically on intact cultured hippocampal neurons are functionally excitatory, triggering action potentials; 4) spontaneous tetrodotoxin-resistant GABAergic synaptic signals in cultured hippocampal neurons form characteristic clusters of kinetics and amplitudes that closely resemble patterns of cholinergic signals at neuromuscular junctions; 5) alternating patterns of clustered properties suggest a dynamic process of GABA release at individual synapses with "quantal" signals involving only several postsynaptic Cl- channels; 6) GABA-A receptors are expressed in virtually all cultured embryonic hippocampal neurons but progesterone metabolite and barbiturate effects are only expressed in subpopulations; 7) fluctuation analysis of GABA-A receptor-coupled Cl- conductance shows complex, two-component kinetics of ion channel behavior in fibroblasts expressing specific alpha-beta GABA-A receptor subunit combinations; 8) some cultured hippocampal and cortical neurons exhibit Lorentzian rather than 1/f noise under baseline recording conditions and this biological noise is sensitive to antagonists at GABA-A receptors; 9) GABA-A agonists stimulate a rise in Cai2+ in cultured embryonic spinal neurons which is dependent on Cao2 +.